quality control assessment methodology related to …
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QUALITY CONTROL ASSESSMENT METHODOLOGYRELATED TO CITRUS DECAY CONTROL
G. Eldon Brown
scieDtific Research DepartmentFlorida Department of citrus
citrus Research and Education CenterLake Alfred
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QUALITY CONTROL ASSESSMENT METHODOLOGY RELATED TO CITRUS DECAY
CONTROL
Control of decay is the major requirement for qood citrus
keeping quality. Fungi that flourish in the high humid! ty and
rainfall environment of Florida can cause extensive decay of
citrus fruit during transit, storage and distribution.
effectiveuse and application of disinfectants andproper
fungicides are of utmost importance for reducing populations
fungi packingof decay in and storage environments
preventing and eradicating infections of the fruit. Knowledge
fungicide strainsof the existence of resistantany
Penicillium digitatum (green mold) within packing and storage
facilities is also necessary to prevent proliferation of decay
caused by this fungus
The purpose of this presentation is to discuss methodoloqy
utilized in decay control practices, including those used to
assay and combat funqicide resistance
Decay Control Chemicals
These kill1. Disinfectants compounds used toare
funqal propaqules present in packinq facilities on floors,
These materials are added to water inwalls, and equipment.
"wet dumps" used to handle fruit, and, in some cases, in water
sprays applied to the fruit. Disinfectants may kill fungal
fruitpropaqules surfaces, but they do not eradicateon
infections like most fungicides do.
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Chlorine This material has been useda.inextensively by the industry surface disinfectantas a
storage rooms, on equipment, and on fruit. In recent years
fruit applications of chlorine have been used to kill canker
bacteria possibly present on the fruit surface. Chlorine has
being inexpensive, it is rapidlyadvantage of but
is pH dependent and corrosiveinactivated by organic matter,
to steel, and it possesses a disagreeable odor.
b. Quaterna~ Ammonium - Quats, as they are commonly
known, are used widely on floors, walls and equipment. These
materials cannot be applied to the fruit. Quats are by nature
wetting agents, and thus have built-in detergency properties
effective of surfaces,penetrantsare porous non
corrosive, stable in the presence of organic matter, but more
expensive than chlorine.
Fungicides - These are chemicals that can be applied2.
directly the fruit and eradicate fungalto to prevent
infections. Some of the materials are slightly systemic and
move a slight distance into the rind after application, thus
protecting fruit infectionsfrom that occur through post-
treatment injuries. Fungicides are commonly applied in water
or in water wax formulations
Benomyl ,Benlate) - This fungicide controls stem-a.end rots (SER) caused by Dielodia and Phomoesis, anthracnose
and blue mold. Because of regulatory changesgreen
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benomyl can no longer be applied postharvest, but it can still
be applied preharvest to control postharvest decay.
- Chemistry and fungicidalThiabendazole (TBZ)b.
activity this fungicide is similar to that of benomylof
it is quite effective anthracnose.except not as on
Thiabendazole is applied only postharvest.
Sodium O-~hen~l~henate (SOPP) - This material isc.best suited for application during washing to clean the fruit.
Fruit is rinsed after treatment and most of the fungicide is
removed except that which accumulates in rind injuries.
of this material during washing helps keep the brushes
sanitary to reduce contamination of healthy fruit. SOPP is
moderately effective against sour rot, but less effective than
benomyl or TBZ against green and blue molds and SER
d. Imazalil- Imazalil is as effective as benomyl or
TBZ against green and blue molds, and will control strains
resistant to those fungicides. Imazalil inhibits sporulation
of green mold and hence prevents soilage. Imazalil is
effective than TBZ benomyl tor the control of SER,or
particularly in degreened fruit.
is volatile. eBi~henyl (di~henyl} Biphenyle. a-
vapor-phase fungi stat that is effective only when sufficient
amounts of it are present in the atmosphere surrounding the
fruit. Biphenyl is impregnated into paper pads or sheets and
it volatilizes from the pads that are inserted into the carton
during packing. Sporulation of Penicillium is reduced by
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biphenyl; therefore it is an effective treatment for soilage
The manufacture of biphenyl has been discontinued,control.
isuntil the present supplymaterial can be usedbut the
utilized, probably within the next two seasons
Metbodoloqy Affecting Efficacy of Decay Control Treatments
formulationschemicalcontrolDecay1. Formulations
should be fresh and pure for maximum activity. All of the
in their formulated state, butfungicides are quite stable
they should never be stored under extremely high temperatures.
The materials should be utilized, if not during the season of
following Liquidduringpurchase, at least the season.
willchlorine is strength 12%, butformulated at a near
Diphenyldeteriorate with time to a concentration near 9%.
pads should be stored at cool temperatures and remain packed
in air tight cartons until the day of use
Wettable powder fungicides such as TBZ should be prepared
by stirring a small quantity of water with the material to
Add additional water, mix, and transferform a smooth paste.
the mixture to a holding tank where it should be continuously
with aeration prevent theagitated mechanically toor
Agitation is especiallyfungicide from settling out.
important in drenchers where some of the fungicide may adhere
Emulsifiablerapidly.soil particles that settleto
concentrate formulations are oily liquids that are not easily
removed from containers. Warm water, in excess of lOO~, can
be used to more thoroughly rinse these containers.
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Treatment Conditions2.Concentration and DH - The concentration, pH anda.
purity of the fungicide should be maintained at the correct
since fungicides applied in non-recovery applicationslevels.
this system is the mostcannot be contaminated before use,
in of applying postharvestpopular method the industry
Wi th SOPP, a non-recovery foam application duringfungicides.
washing has become more popular than a recirculating drench
Because of contamination and lack of easyor spray treatment.
abandonedcontrol, packinghouses havepH most
recirculating system.
SOPP hydrolyzes in water to the undissociated phenol
the dissociated anion (Q-phenylphenate) .phenylphenol and
The undissociated Q-phenylphenol is the active fungicide in
it is phytotoxic certainthe formulation, but above
concentrations. These concentrations lie in the range of 200-
depending upon the treating temperature and period400 ppm,
Higher than ambient temperatures and longer thanof contact.
periods increase phytotoxicity.recommended exposure
amount of Q-phenylphenol in the SOPP solution is dependent
Phytotoxic levels of Q-phenylphenol can even existupon pH.
in 0.5% solutions of SOPP if the pH is allowed to drop (Table
formulationsthis remember that ifFor reason, are1).
diluted to less than 2%, additional buffer must be added to
The principalthe solution to maintain the pH above 11.5.
causes of fruit damage in commercial practice are a drop in
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Relationship between pH and concentration of Q-phenylphenol in solution in sodium Q-phenyl-phenate formulations at 0.5,1.0, and 2.0% (Eckert,Kolbezin and Kramer 1969)
Table 1.
o-phenylphenol in solution (ppm)
SOPP (%)z
1.0 2.00.5
70 14012.0 45
20555 11011.8
170 32011.-6 85
-y Injury10.8 450
6501.0.6
zy
SOPP = sodium Q-phenylphenate.Not determined.
solution dilution of theof the treatment caused by
accumulation acidicsolution additional water, ofwith
such as rotten fruit in recirculating drenches,substances
extended periods of fruit exposure before rinsing, and the use
of harsh, usually new, washer brushes with SOPP on very early,
tender skinned, degreened fruit
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Any water in the packinghouse that is continuously applied
to fruit, such as that in drenchers and soak or dump tanks,
should be treated with chlorine to sanitize it. If not, the
water becomes contaminated with decay organisms, such as those
causing brown and sour rot, and green and blue mold. since
chlorine is rapidly inactivated by organic matter, it must be
continually metered into the tank during use to maintain a
level of 25-50 ppm of free available chlorine. Activity of
the chlorine is dependent upon the presence of hypochlorous
acid which is (Figurecontrolled by pH 1(HOCl) ,
Hypochlorous acid is more biocidal than the hypochlorite ion
(-OCl), and it predominates in solutions at pH 7.5 or less.
However, at pH 6.5 and less, chlorine is more volatile and the
higher levels in the air are irritating to workers. At low
pH, it is also more corrosive to the equipment. Levels of 25-
50 ppm chlorine can be monitored with a chlorine kit that
measures free available chlorine over a range of 10-200 ppm,
and pH can be measured with a pocket pH meter. The meter
should be adjusted with calibration solution before use.
Chlorine willcontent influctuate systems where the
chlorine is metered in at a constant rate. Under very high
At lowfruit treatment rates, chlorine levels will be near O.
usage, chlorine may be in excess of 200 ppm. At low chlorine
levels, effectiveness will be reduced, and at high levels,
some chlorine may be wasted and it will be more volatile and
corrosive. Commercial availablesystems where theare
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chlorine is metered accurately upon demand by measuring the
oxidizing power of the solution, but such systems are more
expensive and have to be evaluated for reliability.
Relationships among hypochlorous acid (HOCIhypochlorite ion (.OCI) and pH (Baker 1959).
Figure 1.
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bin drenchingPallet is usually the only intreatment
Florida packinghouses where the fungicide suspension is
recycled and reused. All other appli~ations are usually non-
recovery. Thiabendazole is the most commonly used material
in drenchers now that benomyl cannot be used for postharvest
application. Concentrations of TBZ should be maintained near
1000 ppm for optimum effectiveness. To retain this level,
fresh TBZ added back to the tank should be at a concentration
of near 1500 ppm. This concentration will vary to some extent
among drenchers depending upon how well the TBZ is kept in
suspension. The concentration of TBZ in the drencher should
be checked weekly. Two relatively simple procedures
available to check TBZ concentrations, but of theseone
requires a UV spectrophotometer. In the other, amine-an
copper reagent in chloroform is reacted with sodium hydroxide
and TBZ. After the water-solvent emulsion separates,
solvent portion is filtered and the clear green chloroform-
TBZ solution is compared with a set of previously prepared
permanent colored standards.
b. Deareening - Degreening favors development of SER
and anthracnose, caused by DiDlodia and Colletotrichum,
respectively. Recommended methods of degreening utilizing
ethylene at about 5 ppm and relative humidities of 90-96%
should be followed to minimize the effect degreening has on
decay. Ethylene concentrations that exceed the recommended
range will not enhance the degreening rate, and they will
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increase disease.significantly inoculatedAnthracnose on
Robinson tangerines increased from 16.7 to 85.9% bywas
degreening with 50 rather than 10 ppm ethylene (Table 2). The
incidence of Diplodia SER in Valencia oranges was increased
significantly by degreening with 50 ppm ethylene, even when
fruit for decay control (Figure 2).treated with TBZwere
if high relative humidityHowever, the levelsproper are
maintained during degreening, the incidence of green mold can
be reduced by the degreening treatment. High moisture levels
promote healing of injuries in the flavedo, thereby protecting
the rind from infection (Table 3). High temperatures also
playa role by retarding the growth of penicillium and
Table 2. Influence of ethylene concentration on theincidence of anthracnose in Robinson tangerinesinoculated with Colletotrichum gloeos~orioides(Brown and Barmore 1977)
Ethylene concentrationsZ(ppm)
Frui t with anthracnose(%)
0 0.0
10 16.7
20 56.7
30 65.5
40 86.7
50 85.9
Z Fruit were exposed to ethylene for 2 days,. and stored for 1week at 7SoF at near 100% relative humidity.
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allowing the healing process to proceed before the fungus has
opportunity invade the injury. low relativeto Atan
humidity, injured tissue desiccates and dies without forming
a barrier to the fungus.
48 72 96HourI
Incidence of stem-end rot caused by Di~olidanatalensis in Valencia oranges treated withthiabendazole (1000 ppm) after exposure toethylene CO, 10, or 50 ppm) for 48, 72 or 96hours and stored for 4 weeks at 85~F and 94-96%relative humidity. Bars represent standarderrors of the means of 3 replications (Brown1986).
Figure 2.
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ADDlication ofc. Time application of decay control
treatments is very critical. Delays in treatment allow fungal
infections at injuries and at the stem-end to penetrate beyond
reach of fungicides that be applied later. Themay
relationship between infection and the time of treatment with
SOPP is shown in Figure 3 where efficacy of the treatment
dropped drastically after 24 hours. Efficacy of the treatment
was less a few hours after inoculation because ungerminated
spores are less sensitive to the fungicide than germinated
ones. Delays between harvest and treatment should not exceed
40-S00F)24 hours unless the ambient temperature is so cold
growth fungi isof the retarded. fruitWhen is de-
greened, treatments following degreening become progressively
less effective the later they are applied after degreening
(Figure 2). Efficacy of all postharvest fungicides against
SER is best with treatments applied before rather than after
degreening (Table 4) . Thus, good fungicide applicationa
before degreening, such as a preharvest spray or postharvest
drench, is much more effective than later applications
Applications on the packingline are most effective when the
fungicides are applied in water. However, some packers prefer
to apply the fungicides in the water wax. The concentration
in the wax should be double that of the water application to
attain comparable efficacy. Even then, movement of imazalil
in the rind is hindered when it is applied in resin solution
water wax. In either water or wax, the fungicide should not
14Table 3.
Fruit infected with greenmold (%) after deqreeninq at:
Degreening temperatureZ(oF)
90-96 RH(%)
55-75 RH(t)
81 89 7186 63 9391 21 97
Q 75..J
50
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01\ I I I I I I
0 5 10 20 30 40 50DELAY BETWEEN WOUND INOCULATION AND TREATMENT (hr)
Figure 3. Effect on time between wound inoculation andtreatment upon the effectiveness of sodium Q-phenylphenate (SOPP) in controlling green mold onoranges. The oranges were submerged in a 2. 0% SOPPsolution pH 12 for 2 minutes and then rinsed withwater (Seberry 1969).
02
zww~c
~
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Table 4. Efficacy of fungicides applied before or afterdeqreeninq for control of stem-end rot caused byDi~lodia natalensis (Brown 1986)
Percentaae decav contrailBefore After
Rate(ppm)Fungicide
Benomyl 600 1.00 91
Thiabendazole 1000 91
97 52
Imazalil 1000 84 63
78 44
Guazatine 1000 86 41
Z Decay control in experiments where fungicides wereapplied as drench treatments to unwashed fruit beforedegreening for 72 hours or as nonrecovery sprays towashed fruit after degreening before waxing.
be applied to excessively wet fruit because the water
dilute the strength of the fungicide and wax. Polisher-drier
brushes tend to remove some of the surface residues left
the fruit from aqueous applications. This may interfere with
sporulation control activity of imazalil. To circumvent this,
application ofan aqueous 1000 be followed withppm can
another application of 1000 ppm in the wax. This will provide
maximum control of infection by utilizing the systemic action
of the aqueous treatment, and the sporulation control provided
by the surface residues that remain from the wax application.
Thorough coverage of the fruit with fungicide must be achieved
during application. This can only occur if all applicator
nozzles or sprays are functioning, and if the fruit has an
opportunity to rotate and contact fungicide-saturated brushes
evenly on all surfaces. This will not occur if the dump rate
exceeds that designed for the equipment, where fruit are so
crowded that they may never contact the brushes
Enough fungicide residue (0.2 - 0.3 ppm) must be deposited
the fruit for control. However, the amount ofon decay
residue is usually timingthe of thenot as important as
fungicide application. Drenches of fungicide before
degreening that leave residues of 0.2 ppm are often much more
effective as decay control treatments than water wax fungicide
applications made after degreening that leave residues of 1.2
ppm. Residues fro.m postdegreening treatments may never reach
invadingthe hyphae Higherof the fungus. residues
important, however, for effective control of sporulation of
fruitR..a. digitatum infected (Table Residues5) .on
imazalil from aqueous applications had to exceed 1 ppm before
sporulation fruitdiseased effectively prevented.on was
Residues from aqueous applications of imazalil provide better
sporulation control of infected fruit thanpenicillium on
comparable residues deposited in water wax.
With diphenyl, some caution has to be observed to prevent
residues from exceeding legal tolerances (U.s., 110 ppm;
European EEC, 70 ppm). Oranges and tangerines absorb at least
twice as much diphenyl per unit of surface area than lemons
1.7
Table 5. Relationship between residues of imazalil fromaqueous applications and control of sporulationof Penicillium diaitatum
Residues (ppm)z Sporulation indexY
0.00
0.89
1.00
1.17 1.6
1.42 0.6
1.45
1.93
2.33
2.81
Residues of imazalil on a whole fruit basis from aqueousnonrecovery applications for 15 seconds.Y Sporulation index: 5 = fruit surface covered entirely with
green sporulating mycelium; 0 = fruit surface withoutmycelium and/or with white nonsporulating mycelium.
or grapefruit, and early green-colored fruit absorb more
diphenyl than more mature, well-colored fruit. with these
varieties and in these instances, one rather than two pads
carton be adequate.per may Diphenyl tends to be less
effective for control of sporulation of Penicillium on
varieties that absorb more material. Since more is absorbed
by the fruit, less diphenyl remains in the atmosphere and
suppression of sporulation is less effective
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d. storage - Low temperature storage maintains fruit
quality and retards development and spread of fungal
infections. Diplodia isDevelopment of rot and SERsour
essentially halted below 40°F. All decay fungi will resume
fruit higherdevelopment transferred back toonce are
temperatures. Keep in mind that grapefruit and lemons are
susceptible to chilling injury and should not be stored below
SO-SSOF for long periods of time. To better identify problems
that may occur after fruit are shipped, representative samples
should be taken after packing and placed in storage at 70-
800F for observation. These can be observed weekly for 2
with withweeks domestic shipments, and at least 4 weeks
fruit. Disordersexport observed arrival at theupon
destination can often be identified from those observed in the
test samples held at the packing source
Fungal Resistance to Fungicides
1. ~e of Resistance - Citrus decay fungi can develop
resistance to postharvest fungicides. E digitatum and .f...,..
italicum (green and blue mold) have frequently caused
commercial losses because of their ability to resist soPp,
diphenyl, imazalil.TBZ, benomyl, and recently, The other
decay fungi, as yet, have not developed resistance. Because
of their ability to produce large numbers of airborne spores,
the mold fungi can rapidly produce large numbers of resistant
spores in packinghouse and storage environments. Potentially,
a single spore of ~ diaitatum can produce about 100 million
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fruit ininfected 7 days under optimumspores on an
environmental conditions. populationIn natural of ~a
digitatum, resistant TBZ or benomyl spores are produced at a
Once TBZ or benomylrate of 1 to 10 per 100 million spores.
is used continuously, the resistant spores infect and multiply
rapidly and eventually replace the sensitive types. since TBZ
are chemically similar,and benomyl strains of Penicillium
resistant to one are usually resistant to the other
Shift of the natural population to resistant under the
selection pressure of the fungicide is reached either through
disruptive solution.directional In disruptivea or a
selection, fungicidethe is essentially inactive against
resistant strains and these proliferate suddenly causing a
quick and sudden loss of disease control. This situation has
happened with TBZ and benomyl. with a directional selection
situation, the loss of fungicide activity is much more gradual
beginning with a few less sensitive strains which increase in
numbers slowly over time. Such directional selection has
occurred with imazalil in California lemon houses.
2. Factors that Favor Develonment of Resistance
Repeated, continuous use of the same fungicide increases the
possibilities developingof resistance problem. Thea
selection exerted by postharvest fungicidepressure a
treatment on citrus fruit is considerably greater than that
produced by the fungicide sprayed in the field.same
Postharvest fungicides are applied in a manner that usually
20
in fungicide depositresults complete and thecoverage,
slightly life of thedeteriorates only during the storage
fruit. The treated fruit are stored under conditions that
permit growth and sporulation of fungicide-resistant strains
The resistant spores are dispersed readilyof the pathogen.
funqicide-air in the packinghouse to otherby currents
selectiontreated fruit, continuing the of forprocess
fungicide resistance.
with the fungicide used in thePre-harvest sprays same
willpackinghouse also enhance the selection forprocess
Pre-harvest sprays of benomyl used in Floridaresistance.
for postharvest decay control may select for strains resistant
to the TBZ application in the packinghouse
storage of treated fruit for extended periods of time give
the resistant strains time to infect, sporulate, and reinfect.
Thus, resistance became a major problem in California lemon
packing, and was also first noted in Florida with lemons. In
both situations, treated fruit are stored for several weeks
or even months. Holding fruit in cold storage for summer sale
is another example where resistance may be manifested. In
most Florida packing operations, treated fruit are shipped
before infected fruit sporulate in the packinghouse. However,
fruit sporulation inwith the storageexport may occur
facilities at the docks, or in transit aboard ship.
isto fungicides3. Assessing Resistance Resistance
evaluated by collecting mold spores from the atmosphere or
from surfaces of walls, floors, and inequipment
packinghouse. These are then dispersed on a culture medium,
that isusually potato dextrose agar-yeast extract-peptone,
amended with the fungicide of interest. Amendments to
media, such as dichloran (3 ppm) or Q-phenylanizole (100 ppm)
and PCNB (500 ppm) , have been used to suppress contaminating
fungi and to cause colonies of penicillium to be compact and
nondiffusive counting. Concentrationsfor easier
fungicides inused the resistance have variedassays
attempts have been made standardizeto these levels so
comparisons among surveys can be made. Recommended levels in
ppm of fungicides for use in the culture media are TBZ
benomyl 2; Q-phenylphenate 15-20; imazalil 0.05-0.1. Spores
are also cultured at the same time on nonamended media so a
measure of the total population can be obtained to determine
the percentage of resistance.
Several methods have been utilized to collect spores.
most common procedure is to remove lids from petri dishes
containing the media, usually for a minute, and to allow the
spores to settle on the agar surface. times areExposure
reduced to 5-15 seconds if spore concentrations are high, such
as at dump sites. Dishes are returned to the lab, incubated
at 75-80oF for several days, and colonies that are formed by
each germinating spore are counted. Another version of this
assay method is to expose filter papers in sterile uncovered
petri dishes for several days at various locations in
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packinghouse. The dishes are covered, returned to the lab,
spores on the papers are removed by washing with sterile
water and measured aliquots of the water are spread over the
surface of agar plates. These are dried, covered, and handled
in a manner similar to the previous procedure. In these two
methods, the assays are used to sample airborne spores that
happen settleto from the atmosphere the exposed teston
techniquessurfaces. These provide indication of thean
contaminationairborne level. anotherIn but more
quantitative method, measured quantities airof drawnare
across the assay media with an air sampler unit. The air
flora impinged directly the surface, and theare on agar
number of spores can be determined per cubic ~oot of air.
When the resistant portion of a relatively high penicillium
population in the packinghouse approaches 10%, performance of
fungicide treatment is usually significantly reduced.
4. Combatting Resistance - Good sanitary practices are
required i! the penicillium population is to be kept at a
minimum in the packinghouse, storage, and transit facilities.
An attempt should always be made to prevent infected fruit
from sporulating in the packinghouse. Irrespective of the
proportion of resistant individuals in the population, if the
total population is minimal then the occurrence of resistance
will be a minor problem. To maintain low inoculum levels, all
infected fruit should be discarded daily and the equipment and
premises withcleaned water and Thisdetergent. becan
23
followed with a spray of an appropriate disinfectant. Cartons
of unshipped fruit with excessive green mold should never be
in but shouldrepacked the packinghouse, be handled at a
separate location where spores cannot be released back into
the packinghouse atmosphere. Repacking may well have been
necessary because resistant strains of ~ digitatum had caused
the decay. A significant reduction in decay has been noted
when the dump and primary grade areas, where decayed fruit are
first encountered, are spatially separated from the rest of
the packingline and loading facilities. Exhaust fans at a
totally enclosed dump can be used to remove spores from the
packinghouse, and packinglinethe be designedcan so
prevailing wind do spreadcurrents not from thespores
degreening lineand dump to the rest of the Aareas
sanitizing of chlorine be applied tospray can spore-
contaminated fruit immediately after dumping to reduce the
inoculum load.
with the loss of benomyl and diphenyl, only three
fungicides available for application.postharvestare now
Fortunately, TBZ, SOPP and imazalil are chemically unrelated
and can be applied in a mixture or in an appropriate sequence
to delay the build-up of penicillium resistance. Resistance
would only for resistance to unrelatedoccur if two genes
fungicides occurred in a single cell, and this is a rare event
in natural population of Use of unrelateda spores.
fungicides is especially valuable when fruit treatedare
24
before and after storage. For example, when a TBZ drench is
fruitapplied to before degreening the drenched fruit can
with SOPP and imazalil.subsequently be treated However,
since imazalil is less effective than TBZ against SER and is
not approved for fruit exported to Japan, much of the drenched
fruit in Florida houses is treated both times with TBZ. Where
it is particularly important to practice goodthis occurs,
sanitation and to monitor the mold population for resistance
If upon assaying for resistance, a significant resistant
population is detected, all efforts should be made to
sanitizethoroughly the house to minimize the loadspore
sanitationstringent should then be practiced, ifand
possible, use of a fungicide of a.different chemistry should
be employed. Benzimidazole resistant strains of ~ digitatum
(green mold) do not compete well with sensitive strains, and
of TBZ is discontinued, resistant populationsonce use
decline. This is not true with blue mold (~italicum), where
strainsresistant have been shown to persist aftereven
discontinuing the use of TBZ. Fortunately, blue mold spore
populations are low in Florida packinghouses.
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residuals. J. Am. Water Works Assoc. 51: 1185-1190.
Bancroft, M. N., Gardner, P. D., Eckert, J. W., and Baritelle,
J. L. 1984. Comparison of decay control strategies in
California lemon packinghouses. Plant Dis. 68: 24-28.
25
Brown, G. E. 1973. Development of green mold in degreened
Phytopathology 63: 1104-1107.oranges.
Brown, G. E. 1984. Efficacy of citrus postharvest fungicides
applied in water or resin solution water wax. Plant
68: 415-418.
Brown, G. E. 1986. Diplodia stem-end rot, a decay of citrus
fruit increased by ethylene degreening treatment and
control. Proc. Fla. state Hort. soc. 99: 105-108.
Brown, G. E. and Barmore, C. R. 1977. The effect of ethylene
on susceptibility of Robinson tangerines to anthracnose.
Phytopathology 67: 120-123.
Ismail,Brown, G. E. , M. A. , and Barmore, c. R. 1978
Lignification of injuries citrusto fruit
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Eckert, J. w. 1988. Dynamics of benzimidazole-resistantI
penicillia in the development of postharvest decays of
citrus and pome fruits. IN: C. J. Delp (ed. Fungicide
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Natural Resources.
26
Eckert, J. w. , Kolbezen, M. J. , and Kramer, B. A. 1969.
Accumulation of Q-phenylphenate by citrus fruit and
pathogenic fungi in relation to decay control and residues.
IN: H. D. Chapman (ed. Proc. 1st Int. Citrus Symp. 2:
1097-1103. Univ. of California, Riverside.
Hall, D. J. and Bice, J. R. 1977. Packinghouse strategies
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Kelly, and Austin,J. L. L. A. 1985. A quantitative
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